Inherit a class from an object?

[tinfanide]

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute" minWidth="955" minHeight="600" creationComplete="init();">
	
	<mx:Script>
		<![CDATA[
			
			
			public function init():void
			{
				
				// how to inherit a known class from the Canvas "box0"?
				var obj:Canvas = new Canvas();
				
				obj.x = box0.x;
				obj.y = box0.y;
				obj.width = box0.width;
				obj.height = box0.height;
				obj.setStyle("backgroundColor",box0.getStyle("backgroundColor"));
				Classroom.addChild(obj);
				
			}
		]]>
	</mx:Script>
	<mx:HBox id="Panel" x="0" y="0" horizontalGap="100" width="100%" height="200">
		<mx:Canvas id="box0" width="200" height="100" backgroundColor="Red"/>				
	</mx:HBox>
	<mx:HBox id="Classroom" x="0" y="100" width="100%" height="90%" backgroundColor="white">
		
	</mx:HBox>
</mx:Application>

If I already know the class of box0 (Canvas), how can obj inherit it from box0?
Like obj.x,
I do not type the exact value of box0.x. Instead, I use box0.x.
How can I do the same in class?